Airblast avalanches

The aerial blast wave from a meteorite impact can trigger dust avalanches in the vicinity, says a new paper published in Icarus. A group of scientists led by Kaylan Burleigh (University of Arizona) reached this conclusion after studying a cluster of five craters that formed in the same impact event, which occurred on an unknown date between May 2004 and February 2006.

SHOCK OVERPRESSURE. The distribution of dust avalanches around this impact cluster follows a two-lobed pattern best explained by the interaction of blast waves in the air. General view at left, the crater cluster top right, and dust avalanches bottom right. (Image: NASA/JPL-Caltech/University of Arizona)

The crater cluster lies 825 kilometers (510 miles) south of Olympus Mons, on part of the wind-eroded Medusae Fossae formation. The largest crater in the cluster is about 22 meters (72 feet) in diameter. Wind-carved ridges called yardangs dominate the area, and it is thickly coated with dust deposits. The crater cluster was captured in image PSP_002764_1800 taken by the HiRISE camera on NASA’s Mars Reconnaissance Orbiter.

By the time the scientists were finished, they had nearly 65,000 dust avalanches counted and classified on yardang slopes within 6 km (4 mi) of the impact cluster. The team expected to find a pattern of avalanches that was symmetrical around the impact cluster, which is what would produced by seismic shock waves traveling radially through the ground after the impact.

Instead, they mapped a dust avalanche pattern that showed two wings shaped like scimitars, one extending south and another, fainter one to the northwest.

They write, “Models of airblasts generated by an obliquely traveling supersonic meteorite in the Martian atmosphere reproduce the “parabolic” scimitar-features we observe.” The meteorite was probably traveling in general west to east direction at an oblique angle.

In the light and dark features of each scimitar wing, the scientists see evidence for airblast waves from the incoming meteorite colliding and interfering with the outflowing blastwave after it struck the ground. Because the impact site shows a tightly spaced cluster of small craters, it is clear the incoming meteorite broke apart before striking the ground. Each piece likely contributed an aerial shockwave to blend and mix with the others.

“Impact-generated airblasts causing tens of thousands of avalanches or slope streaks may constitute a locally important and previously unrecognized process for slope degradation on Mars,” the team concludes.